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alias
What:
-Linux allows a
complex (or commands with long names) to be given a shorter form using a simple
character string
-This is called an alias
-You create aliases
with the alias command
-This command is
built into the Bash shell, not a
separate program
Where:
-usually set in home ~/.bashrc
file (home/username/.bashrc)
-this allows alias to
be used by interactive subshells.
-Aliases that are to
be the defaults for all users are placed in the /etc/bashrc file
How (a) The Rules:
Syntax
alias name-of-alias=value
i.e.
alias r=rm
Rules:
1. No space is allowed
before or after the = (equal sign)
2. If spaces/tabs are
needed then quotation marks (usually single quotes) must be used
i.e.
alias cp='cp -i'
3. Aliases can be
nested, so that you can have aliases that call other aliases.
i.e.
You create two aliases:
alias lll='ls -la'
alias tdr='cd /home/harry'
You can now combine these two aliases to
create another alias:
alias lcd='tdr | lll'
4. Aliases are
disabled for noninteractive shells (i.e. shell scripts)
HOW (B) – PRATICAL USES
Adding Aliases
1) Temporary Alias
To add an alias that
will only last as your current session:
alias lll='ls -la'
2) Permanent Alias – Single User
a) vi /home/user/.bashrc
i.e.
vi /home/Harold/.bashrc
Note: The
file is called .bashrc not bashrc. There is a period (.) at the
beginning of the file
name.
b) Add aliases desired
i.e.
alias lll='ls -la'
c) Save file (ESC,
then qw )
3) Permanent Alias – Root
a) As root:
cd ~
b) Edit .bashrc file
vi .bashrc
c) Add desired aliases
i.e.
alias lll='ls -la'
d) Save file (ESC,
then qw )
4) Permanent Universal Aliases
a) As root:
vi /etc/bashrc
Note: Unlike the other bashrc files, this
has no dot at the front of the file name
b) Go to the end of
the file, put in a comment and add the aliases desired:
i.e.
# Custom Alias for this machine
alias rm='rm -i'
alias mv='mv -i'
alias cp='cp -i'
c) Save file
NOTE: The alias command allows several commands to
be strung together.
Example
As a system
administrator, one of you main jobs will be working with Apache, the main web
server for Linux. As part of this work you will frequently have to look for
Apache (httpd) processes. The standard way to do this is:
ps -ef | grep httpd
Rather than having to
type this over & over again you can create an alias that allows you to do
this in a few key strokes:
alias psh='ps -ef | grep httpd'
List current aliases:
alias
i.e.
root@LocalHostSun Jun 01 > alias
alias cp='cp -i'
alias l.='ls -d .* --color=tty'
alias ll='ls -l --color=tty'
alias ls='ls --color=tty'
alias mv='mv -i'
alias rm='rm -i'
alias which='alias | /usr/bin/which --tty-only --read-alias --show-dot
--show-tilde'
Note: In
this case, nothing follows the alias command. Also some aliases are preset by
the OS.
List value of a specific alias
Type alias alias_name
i.e.
root@LocalHostTue Jun 10 > alias rm
alias rm='rm -i'
Preventing the Shell from Using an Alias
Lets say you have an
alias that is the name of a command (only with options):
i.e.
alias rm='rm -i'
In this case whenever
you type the rm command you will be
prompted for confirmaition (-i).
If you want to run therm command with the –i option then
use the full pathname for the command:
i.e.:
/bin/rm test2
You can also us the \ with the command:
i.e.
\rm test4
Removing Aliases
1) Temporary Alias
Use the unalias command, unalias alias-name
i.e.
You have created the
following alias for the current session:
alias lll='ls -la'
To remove it, do the
following:
unalias lll
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